This invention relates to the forming of non-woven fibrous webs, such as paper webs and more particularly to an improved apparatus and method for the formation of such webs from a dispersion of fibers in a foamed liquid by depositing the liquid and fibers on a forming wire and draining the liquid through the wire to leave the fibers thereon in the form of a web.
The following U.S. patents are representative of the prior art, and are believed material to the examination of this application.
U.S. Pat. No. 3,716,449 discloses formation of a fibrous web, utilizing a dispersion of fibers in an aqueous foam produced in separate mixing units.
U.S. Pat. No. 3,938,782 discloses foamed liquid producing apparatus comprising an inlet and an outlet manifold connected by a plurality of nozzles and reaction tubes cooperatively disposed to generate fluid turbulence.
U.S. Pat. No. 3,871,952 discloses an optimum range of air content for a foamed liquid medium, surface active agents capable of producing the foamed medium, and recovery apparatus for reducing wastage of the surface active agent.
U.S. Pat. No. 3,837,999 discloses a separate foam generator, and a nozzle for directing a foam-fiber dispersion at the juncture of a pair of vertical forming screens.
These prior art patents have in common the teaching of separate foamed liquid generating systems, wherein liquid containing surface active agents are subjected to turbulence in the presence of air to create foam.
U.S. Pat. No. 3,876,498 discloses apparatus including a twin wire wrapped over an impervious breast roll for continuously forming a fibrous web from a slurry of fibers.
U.S. Pat. No. 3,846,232 discloses apparatus including a twin wire wrapped over a fluid pervious suction breast roll for continuously forming a fibrous web from a slurry of fibers.
U.S. Pat. No. 4,062,721 discloses addition of a surfactant to a wet fibrous sheet on a forming wire, and drawing a vacuum across the forming wire and fibrous sheet to form foam in the sheet for expelling water therefrom.
U.S. Pat. No. 3,746,613 discloses a twin wire paper making machine wherein the wires travel in an arc, and water escapes through both wires.
It is a general objective of the present invention to provide improved apparatus and method for the generation of a foamed liquid in a fibrous web forming system that does not require separate turbulence generating devices, yet achieves control of the foamed liquid as to desired air content, viscosity, specific gravity, and related characteristics.
It is a further objective to provide fibrous web forming apparatus including a forming surface, screen, or wire that functions as an element of a turbulence generator producing the foamed liquid.
It is a further and more specific objective to provide fibrous web forming apparatus of the twin forming wire type, wherein one of the forming wires is an element of a turbulence generator for producing foamed liquid within which fibers are dispersed for deposit on the forming wire.